Biodiesel companies and their political allies say Tyson and Houston-based ConocoPhillips won't spend any money to add jobs or new plants, so they shouldn't get the tax break, intended to expand biodiesel production.

"Unless the abuse of this tax credit is prohibited, it will have the exact opposite effect of what Congress intended — it will discourage the creation of real renewable diesel fuel — and all on the taxpayer's dime," U.S. Rep. Lloyd Doggett, D-Texas, said earlier this month.

Doggett has filed a bill to strip away the $1-per-gallon tax credit the Internal Revenue Service extended to ConocoPhillips and other companies with similar plans. The IRS decision broadened a 2005 law passed to promote biofuel production. Dozens of other legislators have signed on to the bill.

In April, Tyson Foods, the Arkansas-based world's largest meat producer, announced it would begin preprocessing animal fat at some of its North American rendering plants this summer. Meanwhile, ConocoPhillips said it would spend about $100 million over several years to produce the fuel. The company plans to introduce the fuel at gas stations in the U.S. Midwest in the fourth quarter of this year.